Hot air convective cooking is achieved by directing rapidly moving heated air at the food. Hot air heated in an air plenum is introduced into the oven cavity via air channels interconnecting the air plenum and the oven cavity. In general, optimal cooking air temperatures are in the 450 F°-500° F. range for non-bakery items, and in the 375° F. range for bakery items.
Infrared (“IR”) heating is another well-known cooking method, whereby electromagnetic waves emitted by a heat source (typically a heating element in the form of a resistance wire) are absorbed by food. Cooking efficiency is achieved by matching the wavelength of the infrared radiation to the absorption characteristics of the food material. In general, IR heating is considered to be most efficient in cooking food when the heating element is at or near 1,200° F.—since the wavelength emitted at that temperature most closely matches food.
So far, attempts to combine heated air and IR heating have achieved limited commercial success due to certain technical challenges as discussed below.
Hot air for cooking food is typically at a temperature (e.g., 450 F°-500° F.) well below the temperature of the IR heating element (ideally at 1,200° F.). Hence, rapidly moving air at a much lower temperature cools the hotter IR heating element in the same oven cavity very quickly. To avoid this problem, an oven having both hot air and IR heating elements needs to separate the airstream from the IR heating element. However, prior attempts to solve this problem were not satisfactory.
For example, U.S. Pat. No. 4,756,091 to Van Denend describes entry of hot air into the oven cavity via tubes, with those tubes being separated from the IR heating elements. However, an IR heating element at a temperature near 1,200° F. emits heat towards the surrounding structure such as air plenum. When the plenum gets hot (such as to 800° F. or more), it is no longer possible to keep the air temperature in the desired range (such as between 450° F. and 500° F.).
Previous attempts to isolate hot air from the IR heating elements have also included the use of IR heating elements which are housed in or shielded behind isolating surfaces made of glass or ceramic, or reflectors, as described in U.S. Pat. No. 6,521,870 to Nolan et al. and U.S. Pat. No. 6,114,664 to Cook et al. However, those attempts did not provide satisfactory solutions because (1) over time, the glass or ceramic surfaces and reflectors became splattered with grease which burned on to that surface and continually degraded the IR emissivity; and (2) ultimately, the glass or ceramic materials chipped or broke, landing on the food being cooked in the oven cavity.